Liquid adsorption process to produce an ultra pure product

ABSTRACT

A process for the etherification and separation of C 3  -C 5  hydrocarbons is improved by the advantageous integration of an oxygenate recovery unit having a 3-bed arrangement into the etherification separation section. A feedstream including C 3  hydrocarbons and isobutene are reacted with methanol in an etherification to produce an etherification effluent that is separated in a first separator into a bottoms stream of MTBE product and an overhead stream of unreacted isobutane, methanol, other oxygenate compounds and C 3  -hydrocarbons. After recovery of methanol, in an adsorptive separation process, the methanol deficient overhead stream enters a second separation zone in the form of depropanizer for the separation of isobutane and higher boiling hydrocarbons from the C 3  hydrocarbons. Any oxygenate compounds that are carried from the bottom of the column with the C 4  + hydrocarbon stream are removed in an oxygenate recovery unit designed to produce an ultra pure product essentially free of oxygenates. A portion of the purified hydrocarbons from the oxygenate recovery unit are recycled as regenerant through the oxygenate recovery unit to desorb oxygenate compounds. This integration of the oxygenate recovery unit provides a closed loop for its regeneration that utilizes existing separation facilities for the removal of oxygenate compounds from the hydrocarbons of the regenerant stream.

This application is a continuation-in-part of copending U.S. applicationSer. No. 717,969, filed Jun. 20, 1991 now abandoned.

FIELD OF THE INVENTION

This invention relates broadly to adsorption processes. In more limitedaspects this invention relates to processes for the production of ethersby the reaction of olefins with an alcohol. In yet more limited aspectsthis invention more directly relates to a process for the etherificationof a dehydrogenation effluent and the recyle materials from theetherification zone to an isomerization zone and to the dehydrogenationzone wherein the unreacted etherification reaction product is recoveredessentially free of oxygenated species prior to subsequent processing.

BACKGROUND OF THE INVENTION

Etherification processes are currently in great demand for making highoctane compounds which are used as blending components in lead-freegasoline. These etherification processes will usually produce ethers bycombination of an isoolefin with a monohydroxy alcohol. Theetherification process can also be used as a means to produce pureisoolefins by cracking of the product ether. For instance, pureisobutylene can be obtained for the manufacture of polyisobutylenes andtert-butyl-phenol by cracking methyl tertiary butyl ether (MTBE). Theproduction of MTBE has emerged as a predominant etherification processwhich uses C₄ isoolefins as the feedstock. A detailed description ofprocesses, including catalyst, processing conditions, and productrecovery, for the production of MTBE from isobutylene and methanol areprovided in U.S. Pat. Nos. 2,720,547 and 4,219,678 and in an article atpage 35 of the Jun. 25, 1979 edition of Chemical and Engineering News.The preferred process is described in a paper presented at The AmericanInstitute of Chemical Engineers, 85th National Meeting on Jun. 4-8,1978, by F. Obenaus et al. Other etherification processes of currentinterest are the production of tertiary amyl ether (TAME) by reacting C₅isoolefins with methanol, and the production of ethyl tertiary butylether (ETBE) by reacting C₄ isoolefins with ethanol.

Due to the limited availability of olefins for etherification, it hasbecome common practice to produce them by the dehydrogenation ofisoparaffins and to pass the dehydrogenation effluent to anetherification process. Processes for producing olefins by thedehydrogenation of saturated hydrocarbons are well known. A typicaldehydrogenation process mixes the feed hydrocarbons with hydrogen andheats the resulting admixture by indirect heat exchange with theeffluent from the dehydrogenation zone. Following heating, the feedmixture passes through a heater to further increase the temperature ofthe feed components before it enters the dehydrogenation zone where itis contacted with the dehydrogenation catalyst. The catalyst zone may beoperated with a fixed bed, a fluidized bed, or a movable bed of catalystparticles. After heat exchange with the feed, the dehydrogenation zoneeffluent passes to product separation facilities. The product separationfacilities will typically produce a gas stream, made up primarily ofhydrogen, a first product stream that includes the desired olefinproducts, and a second potential product stream comprising lighthydrocarbons. The light hydrocarbon stream typically has fewer carbonatoms per molecule than the desired olefin product. Light hydrocarbonsare generally removed from the product stream in order to reduce flowvolume, operating pressures, and undesirable side reactions indownstream process units that receive the olefin product. A portion ofthe hydrogen stream is typically recycled to the dehydrogenation zone toprovide hydrogen for the combined feedstream. The product stream usuallycontains uncoverted dehydrogenatable feed hydrocarbons in addition tothe product olefin. These unconverted hydrocarbons may be withdrawn inseparation facilities for recycle to the dehydrogenation zone or passedtogether with the product olefins to an etherification zone forconversion of the product olefins to ethers.

General representations of flow schemes where a dehydrogenation zoneeffluent passes to an etherification zone are shown in U.S. Pat. Nos.4,118,425 and 4,465,870. More complete representations of a flowarrangement where the dehydrogenation zone effluent passes to anetherification zone are given in U.S. Pat. No. 4,329,516 and at page 91of the October, 1980 edition of Hydrocarbon Processing. The latter tworeferences depict the typical gas compression and separation steps thatare used to remove hydrogen and light ends from the dehydrogenation zoneeffluent before it passes to the etherification zone. A typical effluentfrom an etherification zone includes an ether product, unreactedalcohol, and unreacted hydrocarbon and by-product ethers and alcohols.These effluent components enter separation facilities that yield theether product, alcohol for recycling to the etherification zone, andhydrocarbons for further processing into dehydrogenation. This recyclestream of C₄ or C₅ isoparaffins, prior to recycling to the isomerizationzone and the dehydrogenation zone, is usually treated to recovermethanol and remove other oxygenates which are harmful to theisomerization and the dehydrogenation catalysts.

In the application where isomerization is used to produce moreisoparaffin feed to the dehydrogenation unit U.S. Pat. No. 4,816,607,the recycle stream following the removal of oxygenates is combined withhydrogen and passed to a complete saturation process wherein any olefinand diolefins are saturated. The saturated stream is introduced to afractionation zone along with additional C₄ saturates. A side drawstream comprising normal C₄ hydrocarbons is removed from thefractionation zone and passed over a catalyst in an isomerizationreactor to convert the normal hydrocarbons to isoparaffins. The reactoreffluent comprising isoparaffins is returned to the fractionation zoneand a concentrated stream of isoparaffins is withdrawn from the top ofthe fraction zone and returned to the dehydrogenation zone.

The oxygenate compounds in the etherification zone effluent createproblems such as catalyst deactivation or fouling in downstreamprocesses that receive these unreacted hydrocarbons. For example wherethe unreacted hydrocarbons are recycled to a dehydrogenation zone, MTBEand tertiary butyl alcohol (TBA) may be present in the recycle stream.Oxygenate compounds present in the recycle stream can includeetherification reactants such as alcohols. In particular the incompleterecovery of methanol from the etherification zone exacerbates theproblem by increasing the oxygenate concentration in the recycle stream.

Oxygenates are often removed by adsorption processes. In typicaloperation of an adsorptive oxygenate removal unit the system uses twobeds or multiples of two beds wherein one bed is operating in theadsorption mode and the other is operating in the regeneration mode.

In the adsorption art, 3-bed systems typically are used when the masstransfer zone for a particular separation is longer than one bed. The3-bed configuration has two beds in series during the adsorption mode toallow the mass transfer zone to spill over from the lead bed into thesecond or trim bed in order to more completely load the lead bed to itsequilibrium capacity. At the point of breakthrough from the trim bed,the unused adsorbent capacity remaining in the lead bed has normallyreached less than 25% unused capacity. In a typical application fornatural gas sweetening plants and natural gas dehydrators which exhibitlong mass transfer zones, this lead/trim series configuration can addfrom 5-10% to the capacity of a single bed. A detailed discussion ofadsorption systems including 3-bed configurations is described in anarticle at page 98 appearing in Hydrocarbon Processing, Volume 54, No. 2and at page 86 appearing in Chemical Engineering, Jul. 9, 1973. In theadsorption of oxygenates from a light hydrocarbon mixture of iso andnormal alkanes and alkenes, the mass transfer zone is relatively shortand typically carried out in a single bed or part of a single bed (U.S.Pat. No. 4,814,517). Even though a 3-bed system is disclosed in U.S.Pat. No. 4,734,199 for a liquid phase process for the removal ofmethanol, each bed operates independently in the adsorption mode,although the beds are coupled during a liquid phase regeneration toprovide conservation of the regenerant fluid.

Processes are sought which continuously produce an ultra pure productstream of unreacted hydrocarbons which are essentially-free ofoxygenates. Although single bed systems have been proposed as describedhereinabove, these single bed systems are not resilient to suddenvariations in feed composition such as a spike of oxygenates resultingfrom an upset in upstream processing. In addition, a residual amount ofspent regenerant remaining in an adsorbent bed following regeneration isoften sufficient to contaminate the ultra pure product.

BRIEF SUMMARY OF THE INVENTION

It is a broad object of this invention to provide an effective means forremoving oxygenate compounds to produce an ultra pure stream ofunreacted hydrocarbons. The present invention employs a lead/trimconfiguration with three beds or multiples of three beds wherein eachbed moves cyclically from the trim mode, to the lead mode and then tothe regeneration mode. The function of the trim mode is to provideadditional adsorption media to provide a guard bed to achieve the ultrapure product regenerant in the event of upsets, to provide a greaterutilization of the lead bed adsorbent, and to minimize the potential forproduct contamination during the displacement steps while switchingbetween lead/trim bed positions during the cycle. A critical aspect ofthe invention is the finding that the retention of sufficient capacityin the trim bed at the end of the adsorption step will permit theproduction of the ultra pure product during the switching of the bedfrom trim to lead position.

In the case of the instant invention where there is a requirement for anultra pure product containing between 1 and 0.1 ppm weight ofoxygenates, the trim bed functions as a guard bed providing asignificant safety margin against plant upsets, and further providingincremental capacity to continue producing ultra pure product during theswitching of beds from the trim to the lead position. The 3-bed cycleprovides a more complete capacity utilization of the lead bed, which atthe end of the trim mode in the cycle has reached less than 10% unusedcapacity, while the trim bed still has 90% of its capacity unused. Atthe end of the adsorption cycle in the lead bed, the detectableconcentration of 1 ppm has proceeded less than half the distance throughthe trim bed. Thus, even at a point late in the adsorption cycle, thetwo beds could tolerate a sudden and significant transient surge ofconcentration without experiencing breakthrough to contaminate the ultrapure product. One would not normally consider this cost of equipment andadsorbent justified for a 10% increase in capacity alone.

In a preferred embodiment of the process of the present invention,oxygenates comprising light alcohols and ethers are adsorbed from aliquid hydrocarbon feedstock in the liquid phase to produce an ultrapure product. A liquid hydrocarbon feedstock is passed to a first of twoadsorbent beds simultaneously operating in a lead/trim configuration atadsorption conditions. Each of the adsorbent beds have a feed end and aneffuent end, and each of the adsorbent beds contain a solid adsorbent.The solid adsorbent has a useful capacity and a selectivity for theadsorption of the oxygenates. A mass transfer zone is established in thefirst adsorption bed, and an intermediate stream is withdrawn from theeffluent end of the first adsorbent bed. The intermediate stream ispassed to the feed end of a second adsorbent bed and an ultra pureproduct with an oxygenate concentration of less than 1 ppm weight iswithdrawn from the second adsorbent bed. The above steps are continueduntil the mass transfer zone has proceeded through the first adsorbentbed and is established in the second adsorbent bed at a point where themass transfer zone has used less than about 10% of the useful capacityof the second adsorbent bed. At this point, the passage of thehydrocarbon feedstock to the first adsorbent bed is terminated and thehydrocarbon feedstock is passed to a third adsorbent bed. The thirdadsorbent bed has undergone regeneration and contains a liquidregenerant in the void spaces of the solid adsorbent. As the hydrocarbonfeedstock is passed to the third bed, it displaces the liquid regenerantfrom the third adsorbent bed to provide a displaced liquid regenerant.The displaced liquid regenerant is passed to the first adsorbent bed,and an unadsorbed feedstock stream from the first adsorbent bed ispassed to the second adsorbent bed. The ultra pure product is recoveredfrom the second adsorbent bed for the duration of the displacement. Thepassage of hydrocarbon feedstock to the third adsorbent bed isterminated and the hydrocarbon feedstock is passed to the secondadsorbent bed to provide the intermediate stream. The intermediatestream from the second adsorbent bed is passed to the third adsorbentbed and the ultra pure product is recovered from the third adsorbentbed. The flow of displaced liquid regenerant to the first adsorbent bedis terminated and the first adsorbent bed is isolated. The displacedliquid regenerant is drained from the first adsorbent bed, and asuperheated regenerant vapor is passed to the first adsorbent bed at atemperature effective to desorb oxygenates from the solid adsorbent andrecover the oxygenates from the first adsorbent bed in a spentregenerant vapor stream. The first adsorbent is cooled by passing liquidregenerant to the feed end of the first adsorbent bed and the liquidregenerant is recovered. The flow of liquid regenerant to the firstadsorbent bed is terminated, and periodically, the process cycle isincremented for the second and third adsorbent beds.

Another object of this invention is to provide a method of producing anultra pure stream of unconverted hydrocarbons from an etherificationzone effluent. In a limited aspect a relatively simple and effectivearrangement for separating the effluent from an etherification zone andproviding an isoalkane effluent stream that is essentially free ofoxygenate compounds has been discovered. Thus, in a broad aspect thisinvention charges a feedstream containing saturated and unsaturated C₄-C₅ hydrocarbons to an etherification zone. The etherificationfeedstream includes isoolefins and C₃ hydrocarbons wherein theisoolefins are reacted with a monohydroxy alcohol to produce an etherproduct in an etherification zone effluent that is deficient in thereacted isoolefin. The etherification effluent is separated to recoverthe ether product and the portion of the etherification zone effluentcontaining unreacted hydrocarbons is passed through a methanol recoveryzone for the recovery of methanol and a fractionation zone to remove C₃and lighter hydrocarbons from the stream of unreacted C₄ -C₅hydrocarbons. Lighter oxygenate compounds are removed by thefractionation of the C₃ hydrocarbons. The unreacted C₄ -C₅ hydrocarbonsand the remaining heavier oxygenate compounds is hereinafter referred toas feedstock. Heavier oxygenate compounds are removed by passing thisfeedstock of unreacted hydrocarbons through a separate oxygenaterecovery unit.

In a typical etherification separation as much as 100 wt. ppm heavyoxygenate compounds can be carried over with the unreacted hydrocarbonstream and appear in the feedstock. By the method of this invention, theconcentration of such heavy oxygenate compounds in the unreactedhydrocarbon stream is typically reduced to a range of 10 to 1 ppm wt.and more preferably a range of 1 to 0.1 ppm wt. Such low levels ofoxygenate compounds allow the unreacted hydrocarbon stream to be used asa feed in a variety of processes. One such process is the butaneisomerization of the stream into additional feedstock for thedehydrogenation zone. It is also possible to use this stream as part ofthe feed to an alkylation reaction zone to produce high octane alkylatethat can be used in combination with the MTBE product.

In a more limited embodiment, this invention is a process for producingethers. An etherification feedstream comprising isoolefins andisoalkanes having 4 or 5 carbon atoms is passed to an etherificationzone. The etherification feedstream is combined with a C₁ -C₅monohydroxy alcohol in the etherification zone. The etherification zoneis maintained at etherification conditions to obtain essentiallycomplete conversion of the etherification feedstream and to provide anetherification zone effluent comprising isoalkanes, alcohol, ethers andlight hydrocarbons. The etherification zone effluent is passed to afirst separation zone. At least a first stream comprising an etherproduct and a second stream comprising isoalkanes, light hydrocarbonsand oxygenate compounds, including alcohol and ethers is recovered. Atleast a portion of the alcohol from the second stream is recovered in analcohol recovery zone to provide a recovered alcohol. At least a portionof the recovered alcohol is returned to the etherification zone. Theremainder of the second stream from the alcohol recovery zone is passedto a second separation zone to separate isoalkanes from the secondstream and obtain a third stream comprising isoalkanes and oxygenates.The third stream is passed to an adsorption zone that uses separateadsorbent beds containing a solid adsorbent having void spaces. Thesolid adsorbent has a useful capacity and a selectivity for theadsorption of oxygenates. Two of the separate adsorption beds areoperated simultaneously in a lead/trim configuration at adsorptionconditions. Each of the adsorbent beds has a feed end and an effluentend. The oxygenates are adsorbed in the adsorption zone by passing thethird stream to a first of two adsorbent beds to establish a masstransfer zone in the first adsorbent bed. An intermediate stream iswithdrawn from the effluent end of the first adsorbent bed and passed tothe feed end of a second adsorbent bed. An ultra pure product having anoxygenate concentration of less than 1 ppm wt. is withdrawn from thesecond adsorbent bed. The above adsorption step is continued until themass transfer zone has proceeded through the first adsorbent bed and isestablished in the second adsorbent bed at a point where the masstransfer zone has used less than 10% of the useful capacity of thesecond adsorbent bed. The passage of the third stream to the firstadsorbent bed is terminated. The third stream is passed to a thirdadsorbent bed that has undergone regeneration and contains a liquidregenerant in the void spaces of the solid adsorbent. The liquidregenerant from the third adsorbent bed is displaced by passing thethird stream therethrough to provide a displaced liquid regenerantstream. The displaced liquid regenerant is passed to the first adsorbentbed. An unadsorbed feedstock stream is passed from the first adsorbentbed to the second adsorbent bed and the ultra pure product is recoveredfrom the second adsorbent bed for the duration of the displacement step.The passage of the third stream to the third adsorbent bed is terminatedand the third stream is passed to the second adsorbent bed. Theintermediate stream is recovered from the second adsorbent bed. Theintermediate stream is passed to the third bed and the ultra pureproduct is recovered from the third adsorbent bed. The flow of thedisplaced liquid regenerant to the first adsorbent bed is terminated andthe first adsorbent bed is isolated. The displaced liquid regenerant isdrained from the first adsorbent bed and a superheated regenerant vaporstream is passed to the first adsorbent bed at a temperature effectiveto desorb oxygenates from the solid adsorbent. The oxygenates arerecovered from the first adsorbent bed in a spent regenerant vaporstream. The first adsorbent bed is cooled by passing a liquid regenerantto the feed end of the first adsorbent bed and recovering the liquidregenerant. The flow of liquid regenerant to the first adsorbent bed isterminated and the process cycle for the adsorption and regenerationsteps is periodically incremented for the second and third adsorbentbeds. The ultra pure product is passed from the adsorption zone into thefirst separation zone.

Additional embodiments, aspects and details of this invention are setforth in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of oxygenate removal processarrangement using 3-beds to produce an ultra pure product.

FIG. 2 schematically illustrates a combined dehydrogenationisomerization, and etherification process. This process includes adehydrogenation reactor section 9', an isomerization section 6', anetherification reactor and first separation section 4', a methanolrecovery unit 22', an oxygenate removal unit 21', and a hydrogenationsection 15'.

DETAILED DESCRIPTION OF THE INVENTION

The adsorption process of this invention produces an ultra pure productby the removal of oxygenates in an oxygenate removal unit (ORU) from aliquid hydrocarbon feedstock. The term ultra pure product in thisdescription refers to a C₄ or C₅ hydrocarbon stream which contains lessthan 1 ppm wt. and preferably between 1 ppm wt. and 0.1 ppm wt.oxygenates. The process comprises passing the ORU feedstock to a firstof 3 adsorbent beds or groups of 3-adsorbent beds wherein each bedcontains a solid adsorbent having selectivity of the adsorption of traceamounts of oxygenates. The first and second adsorbent beds are operatedin a lead/trim configuration wherein the liquid hydrocarbon feedstockenters the lead or first adsorbent bed, the effluent of the firstadsorbent bed flows to the feed end of the trim or second adsorbent bed,and an ultra pure product essentially free of oxygenates is withdrawnfrom the second adsorbent bed.

The lead adsorbent bed and the trim adsorbent bed each have a usefulcapacity, or breakthrough capacity. The useful capacity is a measure ofthe total amount of adsorbable material taken up by an adsorbent bed atthe point where the adsorbable material begins to appear in theeffluent. The adsorbent equilibrium capacity is the point when theadsorbent is fully saturated with the adsorbable material. Typically,the adsorption process cycle is stopped before the adsorbent is fullysaturated. The portion of the bed that is not saturated to anequilibrium level is called the mass transfer zone. The parametersaffecting the size and shape of a mass transfer zone are adsorbent type,adsorbent equilibrium capacity, flow rate, packed-bed depth, adsorbentparticle size, physical properties of the carrier fluid, temperature,pressure, and the concentration of adsorbable material in the carrierfluid. If conditions are chosen that are favorable to mass transfer(e.g., long contact time), then the mass transfer zone is small whencompared to the total amount of adsorbent bed employed. In suchconditions, adsorbent bed utilization is more efficient and thebreakthrough (or useful) capacity closely approaches the trueequilibrium capacity. More often, conditions cannot be optimized basedon the adsorbent needs but are fixed by the overall process needs. Thismay dictate unfavorable mass-transfer conditions when practicalpacked-bed diameters and depths must be employed. Actual adsorbent bedutilization is then less efficient and the breakthrough capacity fallsshort of the equilibrium capacity.

In the instant invention, wherein two adsorbent beds are employed in alead/trim configuration, the mass transfer zone moves from the inlet endof the lead bed, travels through the lead bed, and enters the trim bed.The passage of the mass transfer zone in the trim bed is terminated at apoint where the remaining capacity within the trim bed is sufficient toprovide an ultra pure product from an unadsorbed feedstream during thedisplacement period. Preferably, the passage of the mass transfer zonein the trim bed is terminated at a point where the mass transfer zonehas used less than about 10% of the useful capacity of the trim bed andthere is greater than about 90% useful capacity remaining in the trimbed.

In the process cycle of this invention, the passage of the feedstockinto the first adsorbent bed is terminated and the feedstock is passedto a third bed which was recently regenerated and contains a liquidregenerant in the void volume spaces of the solid adsorbent. In adisplacement step, ORU feed is introduced to the third bed and theregenerant in the third bed is transferred from the third bed to thefirst bed which is in the lead position. At the same time the contentsof the first bed comprising unadsorbed feedstock, are displaced to thesecond bed, in the trim position, and a final ultra pure product iswithdrawn from the second bed. At the end of the displacement step, thefirst bed, now filled with liquid regenerant is isolated, and the secondbed is moved to the lead position by the introduction of fresh feedstockto the second bed and the flow of ORU feed to the third bed isterminated. The effluent of the second bed is sent to the third bed,placing it in the trim position, and the ultra pure product is withdrawnfrom the third bed.

The oxygenate recovery unit of this invention uses adsorptive separationto retain the heavier oxygenate compounds. More particularly, theoxygenate recovery unit of this invention is a continuous process forthe liquid phase adsorption of oxygenate compounds combined with thecyclic regeneration of the adsorbent media with a vapor phase regenerantstream of C₃ -C₆ hydrocarbons. Specifically, this invention is a processusing a multiple bed adsorbent zone, preferably having three beds,wherein at least two of the beds are arranged in series comprising alead bed and a trim bed, and at least one other bed is beingregenerated. The feedstock is fed to the lead bed and oxygenate-freeproduct is withdrawn from the trim bed. The operation of the processtakes place in the following sequence when considering the operation ofa single adsorber bed. At the beginning of the cycle in the trim mode(T), the oxygenate-free product is withdrawn from the bed in the trimposition and it receives feed from another bed in the lead position. Thesystem then enters a first displacement (D1) mode wherein product flowfrom the bed in the trim position continues as the remaining unadsorbedfeedstock flows from the lead bed. At the conclusion of the D1 step, thetrim bed is placed in the lead mode (L), wherein feedstock is charged tothe lead bed and the effluent from the lead bed is charged to a newlyregenerated bed now in the trim position. At the conclusion of the leadmode, a second displacement (D2) takes place wherein the bed continuesto provide feed to a bed in the trim position, but the feed to the bedin the lead position is regenerant liquid which displaces the remainingunadsorbed feedstock from the lead bed to another bed in the trim mode.The former lead bed then enters a regeneration mode (R) comprisingdraining of the regenerant liquid; introducing regenerant vapor to heatthe bed and to desorb the oxygenates; and cooling of the bed byintroducing liquid regenerant to the feed end of the bed. At thecompletion of the regeneration cycle, the bed enters the thirddisplacement step (D3) wherein the regenerant liquid is displaced fromthe regenerated bed to another bed now in the lead mode by introductionof feedstock. At the completion of the regeneration cycle, theregenerated bed is returned to the trim mode.

The first bed begins the regeneration procedure with the draining of theliquid regenerant from the first bed. A small amount of superheatedvapor is provided at the top of the first bed to force the liquidregenerant from the bed and recover the regenerant in a separator. Whenthe bed is completely drained, the heating step begins and the full flowof superheated regenerant is passed through the first bed from the topto desorb the oxygenates from the adsorbent. The spent regenerant vaporis condensed and recovered in a separator. A portion of the heatrequired to vaporize the regenerant is recovered by a heat recoverymeans. In the separator, the spent regenerant is separated to provide ahydrocarbon phase comprising regenerant and oxygenates and an aqueousphase comprising oxygenates. The hydrocarbon phase is recovered andreturned to the separation zone in the etherification section. Theaqueous phase is recovered and returned to the separation zone in themethanol removal section of the ether production complex.

At the conclusion of the heating step, the first bed is cooled andfilled with liquid regenerant by passing liquid regenerant to the bottomof the first adsorbent bed and recovering the regenerant in theseparator. At the end of the cooling and fill step the flow ofregenerant to the first adsorption bed is stopped and the above cyclesare begun on the next lead bed.

The above process is most suitable for the removal of trace oxygenatesfrom the effluent of an etherification reaction after the followingprocess steps: the separation of the ether product; the removal of theunreacted alcohol; the removal of C₃ -minus hydrocarbons in a separationzone.

There are two feed materials to the subject process. One of the feedmaterials is a water-soluble alcohol which preferably has less than 4carbon atoms per molecule. Thus, the alcohol can be chosen frommethanol, ethanol, primary and secondary propanol, the various butanols,and other alcohols. However, the preferred class of alcohols are C₄-minus aliphatic monocyclic alcohols with methanol and then ethanolbeing particularly prefered. The majority of the description of theinvention is presented in terms of the reaction of isobutene withmethanol since these are the preferred feed materials and this is thecommercially predominant reaction. However, it is not intended tothereby lessen the scope of the inventive concept. This is especiallytrue since there have been predictions that the expected large demandfor ethers as anti-knock additives will lead to the use of large amountsof ethanol produced by fermentation in the etherification processes.

The second feed materials is a C₄ -C₆ acyclic hydrocarbon or a singlecarbon number mixture of isomeric hydrocarbons. The hydrocarbon feedmaterial may therefore be substantially pure normal butane, normalpentane, or a mixture of the corresponding isomeric and normalhydrocarbons. The preferred hydrocarbon feedstream is a mixture ofisobutane and normal butane such as is available from several sources ina petroleum refinery or as is available as field butanes. This varietyof possible feed materials allows the production of a wide variety ofethers other than the preferred MTBE including methyl tertiary amylether, ethyl tertiary amyl ether, and ethyl tertiary butyl ether.

In a more limited embodiment, this invention is a process for producingMTBE that has an oxygenate removal unit for recovering an essentiallyoxygenate free recycle stream that is recycled to an isomerization zoneand a dehydrogenation zone. In the process a recycle stream and afeedstream are combined to provide a dehydrogenation zone input stream.The feedstream comprises isobutane and hydrogen. The input stream iscontacted with a dehydrogenation catalyst at dehydrogenation conditionsin a dehydrogenation zone to obtain a first effluent stream comprisingisobutene, isobutane, hydrogen and hydrocarbons having less than 4carbon atoms. At least a portion of the first effluent stream is passedinto a hydrogen recovery section to remove hydrogen from the firsteffluent. The first effluent from the hydrogen recovery section ispassed to an etherification zone where it is combined with methanol andcontacted in an etherification zone with an etherification catalyst atetherification conditions to react essentially all of the isobutene andobtain a second effluent stream comprising isobutane, MTBE, methanol,dimethylether, tertiary butyl alcohol, TBA, other oxygenate compounds,water and hydrocarbons having less than 4 carbon atoms. The secondeffluent is separated in a first separation zone in the etherificationzone to produce an MTBE product stream containing a majority of the TBAand a separator stream that comprises isobutane, methanol, DME, TBA andwater and other oxygenates, and includes hydrocarbons having less than 4carbon atoms. The separator stream is passed to a methanol recovery zonethat recovers a majority of the methanol from the separator stream. Atleast a portion of the methanol from the methanol recovery zone isreturned to the etherification zone. The remainder of the separatorstream is passed to a second separation zone in the methanol recoveryzone and separated into an overhead stream comprising C₃ hydrocarbonsand lower boiling compounds comprising DME and water and a bottomsstream comprising oxygenate compounds. The bottoms stream is passed toan oxygenate removal zone comprising a 3-bed adsorption system andcontacted therein with an adsorbent that selectively absorbs theoxygenate compounds and produces a recycle stream that is ultra pure andis essentially free of oxygenate compounds. Two beds of the 3-bedadsorption system operate in series while the third bed periodically isregenerated by passing at least a portion of a saturated recycle streamto the oxygenate recovery zone as a regenerant stream to desorboxygenate compounds from the oxygenate recovery zone. The desorptionstream is passed to the first separation zone for recovery of oxygenatecompounds. The recycle stream is combined with hydrogen and passed to acomplete saturation unit which catalytically saturates any remainingolefins and diolefins in the recycle stream to produce a saturatedrecycle stream. The saturated recycle stream is passed to adeisobutanizer column, wherein a stream of mixed butanes containing isoand normal butanes is introduced as feed, and a C₅ + stream is withdrawnfrom the bottom of the deisobutanizer column. At least a portion of thenormal butane in the column is withdrawn as a side draw from thedeisobutanizer and passed to a dryer to provide a dry normal butane feedfor the isomerization reactor. The effluent from the isomerizationreactor is returned to the deisobutanizer at a point in thedeisobutanizer above where the normal butane side draw was made.Isobutane is withdrawn from the top of the deisobutanizer and recycledto the dehydrogenation zone.

The invention is illustrated by the following process description modewith reference to the flow diagram of FIG. 1 of the drawings. Thefeedstock being treated in this illustrative process is the unreactedeffluent from an MTBE unit which has undergone three separations toremove MTBE, to recover methanol and to remove light C₃ -components. Theetherification effluent is obtained by the catalyzed reaction ofisobutylene with a stoichiometric excess of methanol in the liquid phaseat a temperature of about 65 to about 90° C. The isobutylene reactant isintroduced into the reactor as a mixture of trans butene, butadiene,isobutane and n-butane. The isobutylene constitutes about 45 mol. % ofthe C₄ hydrocarbon mixture, and is the only C₄ species which reacts withthe methanol under the present conditions. The molar ratio of methanolto isobutylene is from about 1.05:1 to 1.5:1. The effluent from thereactor comprises product MTBE, unreacted methanol, unreacted C₄ 's andsmall to trace amounts of dimethylether. TBA and other reactionby-products. This effluent is passed to a distillation unit wherein theMTBE product is recovered from the bottom. The overhead effuent from thedistillation unit is typically water washed or passed to a separateadsorber unit to recover the bulk of the unreacted methanol from theetherification reaction and return the methanol to the etherificationreaction zone. The resulting raffinate has the following typical amountsof oxygenates:

    ______________________________________                                        Dimethylether          50 ppm                                                 Water                  50 ppm                                                 Methanol                5 ppm                                                 TBA                    50 ppm                                                 MTBE                   10 ppm                                                 ______________________________________                                    

and is hereinafter referred to as the ORU feedstock. In the operation ofthis illustrative process, the overall cycle time requires 4320 minutes,i.e., the time interval from the beginning of an adsorption-purificationstep in one of the adsorption bed until the beginning of the nextadsorption-purification step in the same bed.

With respect to FIG. 1, the liquid hydrocarbon feedstock enters thesystem through line 1. In a typical cycle, the liquid hydrocarbonfeedstock first enters an adsorber bed 101 through lines 3, 4 and 5 at arate controlled by valve 201. Adsorber bed 101 contains a zeoliticmolecular sieve adsorbent having the capacity to adsorb trace quantitiesof oxygenates comprising methanol, MTBE, tertiary butyl alcohol (TBA),dimethylether, and water. Oxygenate selective adsorbents are used forthe removal of these oxygenates from the hydrocarbons. A wide variety ofadsorbents including activated alumina, silica gel and zeolite molecularsieves have been proposed for this class of separation. Zeoliteadsorbents particularly zeolite 5A, zeolite 13X and zeolite D arepreferred. It has also been taught in U.S. Pat. No. 4,814,517, theteachings which are hereby incorporated by reference, that a combinationof silica gel and zeolite 13X in an adsorbent bed will provide superioradsorption of oxygenate compounds. A most preferred adsorbent for thispurpose is the commercial zeolite widely known as zeolite 13X.

The temperature within adsorbent bed 101 is 26°-38° C. and pressure of150 psig. Immediately prior to the introduction of the feedstock toadsorber bed 101, the bed was operating in the trim position, acceptingfeedstock from the lead bed and producing an ultra pure product. Beforethe feedstock entered the adsorber bed 101, all the beds in the systemunderwent a hereinafter described displacement step.

Feed passes through the bed 101 and the effluent from bed 101 is carriedvia lines 6 and 19 to valve 207 and from valve 207 through lines 20, 22and 18 to adsorber bed 102 which is operating in the trim position. Theultra pure product essentially free of oxygenates is removed fromadsorber bed 102 via lines 15 and 16, through valve 214, and lines 17, 9and 10. Thus, adsorber beds 101 and 102 are initially operating inseries in a lead/trim configuration. At the same time adsorbent bed 103is in the regeneration mode. At the end of the lead period for adsorbent101, the beds in the system undergo a displacement step. After thedisplacement step, adsorbent bed 102 shifts from the trim position tothe lead position, adsorbent bed 101 formerly operating in the leadposition will move to the regeneration position, and adsorbent bed 103will move into the trim position. Just prior to the displacement stepadsorbent bed 103, at the end of its regeneration cycle, contains aliquid regenerant, adsorbent bed 101 contains unadsorbed feedstock inthe void spaces of the solid adsorbent, and adsorber bed 102 contains aportion of unadsorbed feedstock. As the displacement step begins, freshfeedstock is introduced to bed 103 via lines 1, 26, and 27, throughvalve 205 and through lines 28, 29 and 30. The regenerant fluid,initially in bed 103, is passed through lines 52, 53, 51, through valve209 and lines 56, 4 and 5 to adsorbent bed 101. This step transferringthe regenerant fluid to the lead bed prepares it for the regenerationcycle. Adsorbent bed 101 containing unadsorbed feedstock in the voidspaces of the adsorbent, now passes this unadsorbed feedstock to theformer trim bed, adsorbent bed 102, via lines 6, 19, valve 207, andlines 20, 22 and 18. Throughout the displacement step, ultra pureproduct is withdrawn from adsorbent bed 102 via lines 15 and 16, throughvalve 214 and on to lines 17, 9 and 10. Because adsorbent bed 102 hadonly a small amount of its useful or breakthrough capacity utilized,there is sufficient useful or breakthrough capacity remaining within theadsorbent bed in the trim position to continue to produce ultra pureproduct from the unadsorbed feedstock displaced from the lead adsorbentbed during this displacement step. At this point in the cycle, the masstransfer zone has used less than about 10% of the useful capacity of theadsorbent bed 102 and there is greater than about 90% of the usefulcapacity remaining in adsorbent bed 102. At the end of the displacementstep, adsorbent 101 is isolated in preparation for the regenerationstep, and feedstock flows through adsorbers 102 and 103. The ultra pureproduct is withdrawn from adsorbent 103 now in the trim position vialines 52 and 54, through valve 216 and on to lines 55 and 10. Valve 214is closed at the end of the displacement step, and the effluent ofadsorber bed 102 now in the lead position flows via lines 15, 57, valve208, lines 58, 29 and 30 into adsorber bed 103. Valve 205 is closed andfeed flows via lines 1, 26 and 25 to valve 203, lines 21 and 22 and 18to enter bed 102.

Turning now to adsorber bed 101 which was isolated at the end of thedisplacement step. In accordance with this invention, oxygenatecompounds are periodically desorbed from the adsorbent using ahydrocarbon regenerant stream. The regenerant stream compriseshydrocarbons having at least four carbon atoms and an oxygenateconcentration of 1 to 0.1 wt. ppm. Sources of this regenerant streaminclude the purified hydrocarbon stream from the oxygenate recovery unitand C₄ +hydrocarbon feedstreams. A portion of the purified hydrocarbonstream from the oxygenate removal zone is a preferred regenerant streamsince it is deficient in unsaturated hydrocarbons. In order to furtherreduce the presence of unsaturates the regenerant stream is morepreferably taken as an effluent from a hydrogenation unit. Adsorbent bed101 will be regenerated in the vapor phase through the following threesteps: pressure assisted drain, heating, and cooling. A small portion upto 20% of regenerant from line 2 is passed through line 40, throughexchanger 105 and along line 44 to superheater 104. In superheater 104,the small portion of liquid regenerant is superheated to a temperatureabove 240° C. and the vapor is passed along line 45 through valve 218and along lines 46, 48, and 12 to valve 213. From valve 213 the smallamount of vapor passes through lines 11 and 6 and forces the regenerantliquid out of adsorbent bed 101 through lines 5 and 34, through valve202 and along lines 35, 36 and 37 before it joins the remainder of theregenerant at line 41 and travels through valve 210 to line 42, throughcross-exchanger 105 and on to line 43, past condenser 106 and iscollected in separator 107 via line 61. When adsorbent 102 is at thispoint in the cycle, the liquid regenerant flows through lines 18, 23 and24 controlled by valve 204 before joining line 36. Similarly, whenadsorbent bed 103 is at this point in the cycle, the liquid regenerantflows through lines 30, 31 and 32 controlled by valve 206, beforejoining line 37. When the heating cycle is complete, adsorbent bed 102begins a cooling cycle, wherein liquid regenerant is now brought in fromline 2 through line 39, through valve 211 and lines 38, 37, 36 and 35.After all the regenerant has been drained from adsorbent bed 101, thefull flow of regenerant is passed from line 2 through line 40 andexchanger 105 and through line 44 to superheater 104 where all theregenerant is now heated to a temperature in the range of 200°-300° C.The superheated vapor then travels via line 45, valve 218, lines 46, 48and 12, reaching valve 213 and on through lines 11 and 6 to reachadsorbent bed 101. The heated vapor passes through adsorbent bed 101,desorbing the previously adsorbed oxygenates and removing them via lines5 and 34 to valve 202, through lines 35, 36, 37, 41, past valve 210 toline 42 and through cross-exchanger 105. As the flow of vapor throughadsorbent bed 101 continues, there is the potential to recover some ofthe heat of vaporization through cross-exchanger 105 as the cycle ofheating continues. From cross-exchanger 105, the vapor travels to line43 and condenser 106 where the material is condensed and transferredalong line 61 to tank 107.

In producing an ultra pure product, it is important not to recycle anyportion of the spent regenerant within the system during theregeneration process. Therefore, this spent regenerant, or desorptionstream, is passed to another portion of the etherification complex suchas the first separation zone wherein the recovery of the concentratedoxygenate compounds is possible. Spent regenerant leaves the oxygenaterecovery unit from tank 107 via line 63 to pump 108 and is transferredfrom the unit via line 64.

When the heating cycle is complete, adsorbent bed 101 begins a coolingcycle, wherein liquid regenerant is now brought in from line 2 throughline 39, through valve 211 and lines 38, 37, 36 and 35. The liquid thenpasses through valve 202 and lines 34 and 5 and flows up throughadsorbent bed 101. As the first amount of liquid regenerant reaches theheated adsorbent bed 101, some of the regenerant vaporizes and providessome sensible cooling to the adsorbent bed. As the cooling processcontinues, the liquid regenerant is passed through the adsorbent bed 101through line 6, line 11, valve 213, lines 12, 48 and 47 to valve 219.When adsorbent bed 102 is in this mode, the liquid regenerant is passedfrom adsorbent bed 102 through lines 15, 14, and 13 as controlled byvalve 215 to join line 48. Similarly, when adsorbent bed 103 is in thismode, the liquid regenerant is passed from adsorbent bed 103 throughlines 52, 50, and 49, as controlled by valve 217 to join line 48. Fromvalve 219, the regenerant fluid flows along line 59 to line 60 where itpasses through condenser 106. In condenser 106, initially the vaporizedregenerant is condensed and sent via line 61 to tank 107. As the coolingprocess continues, the liquid regenerant having passed through adsorbent101 travels the same path yet condenser 106 functions simply to producea constant temperature for the collection of this material in tank 107.As with the condensed vapor regenerant during the heating process, theliquid regenerant collected during the cooling process is returned vialine 63 from tank 107 through pump 108 and on line 64 to the separationsection in the etherification zone for the recovery of the concentratedoxygenates. At the conclusion of the cooling step, the system againundergoes a displacement moving the current trim bed, adsorbent bed 103,to the lead position, adsorbent bed 101 to the trim position, andadsorbent bed 102 to the isolated regeneration steps. When adsorbent bed102 is in the trim position, the ultra pure product is withdrawn fromadsorbent bed 102 through lines 6 and 7, valve 212 and lines 8, 9 and10.

In a typical application, the time required for a lead adsorption stepor a trim adsorption step is 1440 minutes which is equivalent to a fullregeneration cycle on a single adsorbent bed. The time required for allthree beds to cycle through one complete sequence is 4320 minutes. Thetime for the pressure assisted drain step was 39 minutes, the heatingstep required 975 minutes, the cooling step required 420 minutes, andthe displacement step required 6 minutes. The temperature of thesuperheated regeneration vapor ranged from 200°-300° C. The means forheating the regenerant material could range from a combination of lowpressure and high pressure steam exchangers to a combination of steamexchangers and fired heaters or whatever means necessary to vaporize andsuperheat the regenerant to maintain the conditions necessary to desorbthe oxygenates from the adsorbent undergoing regeneration.

The purified heavy hydrocarbon stream from the oxygenate recovery unitis further processed to increase its octane value. Downstream processesmost commonly used are alkylation for making a high octane hydrocarbonsfor direct use as motor fuel components and dehydrogenation forproducing additional isoalkene feed that is recycled to etherificationzone. Suitable arrangements for alkylation and dehydrogenation are wellknown to those skilled in the art and require no additional explanation.An especially useful recycling combination of dehydrogenation,isomerization and etherification for the production of MTBE is shown inU.S. Pat. No. 4,816,607 and uses a deisobutanizer column to separate anisobutane overhead stream and a normal butane sidecut stream from amixed C₄ feedstream, an isobutane recycle stream from the etherificationzone and an isobutane effluent stream from an isomerization zone.

A broad range of catalysts are commercially available for thehydrogenation zone. Suitable catalyst for this process will completelysaturate mono-and polyolefinic hydrocarbons without significant crackingor polymerization activity. Such catalysts will normally comprise one ormore metallic components which may be elemental metal or a metalcompound. The metals are normally chosen from Groups VIII and IVA of thePeriodic Table of the elements with Ni, Pd, Pt, Sn, being common metalsin these catalysts. Pt is a preferred metal in these catalysts. Based onthe weight of the metal, the catalyst may contain from 0.1 to 4.0 wt. %metallic components. The metallic components of the catalyst aresupported by a refractory inorganic oxide material such as one of thealuminas, silica, silica-alumina mixtures, various clays and natural orsynthetic zeolitic materials. Preferably, the carrier material isalumina. Metallic components may be added to the carrier which is in theform of spheres, pellets or extrudates by impregnation, cogelation orcoprecipitation. Preferably, the metallic components are impregnated byimmersion of an extruded particle in an aqueous solution of ametal-containing compound and thereafter treating the impregnatedparticle by drying, calcination or other treatments.

In another aspect of the invention illustrated by the following processdescription made with reference to the flow diagram of FIG. 2 of thedrawings: the instant invention is shown as a component of an integratedscheme for the production of methyl tertiary butyl ether from a mixtureof butanes. The mixed butane feed comprising iso and normal butane arecharged via line 1' to a deisobutanizer column 2' wherein the isobutaneis taken overhead as stream 8' and passed to a dehydrogenation reactionand separation section 9', wherein hydrogen is collected, a portion ofwhich is sent via line 11' to a hydrogenation step 15'. The output fromthe dehydrogenation section consisting largely of isoolefins of the C₄range and C₃ and lighter hydrocarbons is sent via line 10' to anetherification section and first separation section 4' wherein the MTBEis produced by the reaction of isoolefin with a mole excess of methanolover a catalyst.

In the preferred etherification process for the production of MTBE,essentially all of the isobutene is converted to MTBE therebyeliminating the need for separating that olefin from isobutane. As aresult, downstream separation facilities are simplified and operatedmore economically since these facilities need to handle a reduced volumeof closely boiling materials. Several suitable etherification processeshave been described in the available literature, with these processesbeing presently used to produce MTBE. The preferred form of theetherification zone is similar to that described in U.S. Pat. No.4,219,678. In this instance, the isobutene containing stream 10',methanol feedstream 12' and a recycle stream 25' containing recoveredexcess alcohol are passed into the etherification zone 4' and contactedwith an acidic etherification catalyst at etherification conditions.

A wide range of materials are known to be effictive as etherificationcatalysts reactants including mineral acids such as sulfuric acid, borontrifluoride, phosphoric acid on kieselguhr, phosphorus-modifiedzeolites, heterpoly acids, and various sulfonated resins. The use of asulfonated solid resin catalyst is preferred. These resin type catalystsinclude the reaction products of phenolformaldehyde resins and sulfuricacid and sulfonated polystyrene resins including those cross-linked withdivinylbenzene. Further information on suitable etherification catalystsmay be obtained by reference to U.S. Pat. Nos. 2,480,940, 2,922,822, and4,270,929 and the previously cited etherification references.

A wide range of operating conditions are employed in processes forproducing ethers from olefins and alcohols. Many of these include vapor,liquid or mixed phase operations. The etherification zones contains asulfonated solid resin catalyst and operates at a temperature in therange of from 30°-100° C. (85°-212° F.) and a pressure of from 10 to 40bars. Processes operating with vapor or mixed phase conditions may besuitably employed in this invention. The preferred etherificationprocess uses liquid phase conditions. The reactor effluent of theetherification process is passed to a first separation zone wherein theMTBE product is withdrawn by line 13' and the unreacted isoalkanes aswell as trace oxygenate by-products and unreacted methanol are recoveredand passed via line 3' to the methanol recovery section and secondseparation section 24'. In the methanol recovery section, the unreactedmethanol is removed and returned to the etherification section 4' asstream 25'.

After the recovery of methanol, the remainder of the etherificationeffluent enters a second separation zone which divides the material intoa lower boiling stream 16' of hydrocarbons and light oxygenate compoundsand a higher boiling stream 21' comprising heavy oxygenate compounds andC₄ or heavier hydrocarbons that are suitable for further processing.This higher boiling stream 21' now comprising isoalkanes and traceoxygenates are taken to an oxygenate removal section 20' wherein theultra pure 3-bed oxygenate removal process is practiced. The oxygenatecontaining regenerant is returned to the first separation zone 4'.

The separation zone removes recovered oxygenate compounds from theregenerant stream and the process. Heavier oxygenate compounds leave theseparation zone with the ether product. Some of these heavy oxygenatecompounds are product ethers, the recovery of which increases theproduct yield. Most other non-product oxygenate compounds are acceptablein the product stream so that the product stream offers these oxygenatesa convenient collection point. Any lighter oxygenate compounds thatenters the first separation section with the regenerant are againcarried overhead from the first separation zone and either recovered inalcohol recovery unit or carried overhead with the light overhead of thesecond separation zone. The oxygenate-containing regenerant stream canenter the second separation zone directly or indirectly. For example thespent regenerant stream can be passed with the etherification feed intothe etherification zone and passed into the separation zone via line 26'as part of the etherification effluent. The ultra pure product, stream19', is then sent to a hydrogenation section where any remaining dieneor olefin bonds are saturated and a completely saturated product is sentvia line 17' to the deisobutanizer 2'. A sidedraw, withdrawn as stream14' and comprising normal alkanes, is sent through dryers 16' to line18' and from line 18' to isomerization section 6'. The isomerizationsection contains a catalyst system which is deleteriously effected byboth water and the presence of trace amounts of oxygenates. It ispreferred that the oxygenates coming to section 6' be in concentrationsranging from 1 to 0.1 ppm wt. After isomerization over a platinumcontaining catalyst, the isomerized butane is returned via stream 5' toa point in the deisobutanizer above where the sidedraw stream 14' wastaken. A stream of C₅ + hydrocarbons is withdrawn from the bottom of thedeisobutanizer as stream 7'. This stream prevents the build-up ofheavier hydrocarbons in the system.

What is claimed is:
 1. A process for the liquid phase adsorption ofoxygenates comprising light alcohols and ethers from a liquidhydrocarbon feedstock to produce an ultra pure product comprising:(a)passing said liquid hydrocarbon feedstock to a first absorbent bed oftwo adsorbent beds simultaneously operating in a lead/trim configurationat adsorption conditions, each of said adsorbent beds having a feed endand an effluent end, and each of said adsorbent beds containing a solidadsorbent having a useful capacity and a selectivity for the adsorptionof said oxygenates to establish a mass transfer zone in said firstadsorbent bed, and withdrawing an intermediate stream from the effluentend of said first adsorbent bed; (b) passing said intermediate stream tothe feed end of a second adsorbent bed and withdrawing an ultra pureproduct having an oxygenate concentration of less than 1 ppm wt. fromsaid second adsorbent bed; (c) continuing steps (a) and (b) until themass transfer zone has proceeded through said first adsorbent bed and isestablished in said second adsorbent bed at a point where the masstransfer zone has used less than about 10% of the useful capacity ofsaid second adsorbent bed; (d) terminating the passage of saidhydrocarbon feedstock to said first adsorbent bed and passing saidhydrocarbon feedstock to a third adsorbent bed that has undergoneregeneration and contains a liquid regenerant in the void spaces of saidsolid adsorbent, displacing said liquid regenerant from the thirdadsorbent bed by passage of said feedstock therethrough to provide adisplaced liquid regenerant and passing said displaced liquid regenerantto said first adsorbent bed, and passing an unadsorbed feedstock streamfrom said first adsorbent bed to said second adsorbent bed andrecovering the ultra pure product from said second adsorbent bed for theduration of the displacement; (e) terminating the passage of saidhydrocarbon feedstock to said third adsorbent bed and passing saidhydrocarbon feedstock to said second adsorbent bed to provide theintermediate stream, passing said intermediate stream to said thirdadsorbent bed and recovering the ultra pure product from said thirdadsorbent bed; (f) terminating the flow of said displaced liquidregenerant to said first adsorbent bed and isolating said firstadsorbent bed, draining said displaced liquid regenerant from said firstadsorbent bed, passing a superheated regenerant vapor to said firstadsorbent bed at a temperature effective to desorb oxygenates from thesolid adsorbent, recovering said oxygenates from said first adsorbentbed in a spent regenerant vapor stream, and cooling said first adsorbentbed by passing said liquid regenerant to the feed end of said firstadsorbent bed and recovering said liquid regenerant; and, (g)terminating the flow of the liquid regenerant to said first adsorbentbed and periodically incrementing the process cycle of steps (d)-(f) forsaid second adsorbent bed and said third adsorbent bed.
 2. The processof claim 1 wherein the absorbent for the adsorbent beds in an activatedalumina or a zeolitic molecular sieve.
 3. The process of claim 1 whereinthe adsorbent for the adsorbent beds is zeolite 13X.
 4. The process ofclaim 1 wherein the adsorbent beds operate at adsorption conditionsincluding a temperature of between 30° and 60° C.
 5. The process ofclaim 1 wherein the temperature of the superheated regenerant is between240° and 315° C.
 6. The process of claim 1 wherein said regenerant issaturated ultra pure product.
 7. The process of claim 1 wherein theultra pure product contains between 1 and 0.1 ppm wt. oxygenates.
 8. Theprocess of claim 1, step (d) wherein the first adsorbent bed is drainedby passing a portion of the superheated regenerant vapor stream to theeffluent end of said first adsorbent bed to force the displaced liquidregenerant from said first adsorbent bed.
 9. The process of claim 1further comprising condensing the spent regenerant vapor stream toprovide a hydrocarbon phase comprising regenerant and oxygenates and anaqueous phase comprising oxygenates and recovering said hydrocarbonphase and said aqueous phase.
 10. A process for producing etherscomprising:(a) passing an etherification feedstream comprisingisoolefins and isoalkanes having four or five carbon atoms to anetherification zone; (b) combining the etherification feedstream with aC₁ -C₅ monohydroxy alcohol in said etherification zone at etherificationconditions to obtain essentially complete conversion of saidetherification feedstream and to provide an etherification zone effluentcomprising isoalkanes, alcohol, ethers and light hydrocarbons; (c)passing said etherification zone effluent to a first separation zone andrecovering at least a first stream comprising an ether product and asecond stream comprising isoalkanes, light hydrocarbons and oxygenatecompounds including alcohol and ethers; (d) recovering at least aportion of said alcohol from said second stream in an alcohol recoveryzone to provide a recovered alcohol and returning at least a portion ofthe recovered alcohol to said etherification zone; (e) passing theremainder of said second stream from said alcohol recovery zone to asecond separation zone to separate isoalkanes from said second streamand obtain a third stream comprising isoalkanes and oxygenates; (f)passing said third stream to an adsorption zone that uses separate bedscontaining a solid adsorbent having a useful capacity and a selectivityfor the adsorption of oxygenates and simultaneously operating two of thebeds in a lead/trim configuration at adsorption conditions, each of saidadsorbent beds having a feed end and an effluent end, for the adsorptionof oxygenates said adsorption zone operating by:(i) passing said thirdstream to a first absorbent bed of two adsorbent beds to establish amass transfer zone in said first adsorbent bed, and withdrawing anintermediate stream from the effluent end of said first adsorbent bed,passing said intermediate stream to the feed end of a second adsorbentbed and withdrawing an ultra pure product having an oxygenateconcentration of less than 1 ppm wt. from said second adsorbent bed;(ii) continuing step (i) until the mass transfer zone has proceededthrough said first adsorbent bed and is established in said secondadsorbent bed at a point where the mass transfer zone has used less thanabout 10% of the useful capacity of said second adsorbent bed; (iii)terminating the passage of said third stream into said first adsorbentbed and passing said third stream to a third adsorbent bed that hasundergone regeneration and contains a liquid regenerant in the voidspaces of said solid adsorbent, displacing said liquid regenerant fromthe third adsorbent bed by passage of said third stream therethrough toprovide a displaced liquid regenerant and passing the displaced liquidregenerant to said first adsorbent bed, and passing an unadsorbedfeedstock stream from said first adsorbent bed to said second adsorbentbed and recovering the ultra pure product from said second adsorbent bedfor the duration of the displacement; (iv) terminating the passage ofsaid third stream to said third adsorbent bed and passing said thirdstream to said second adsorbent bed, recovering the intermediate streamfrom said second adsorbent bed and passing said intermediate stream tosaid third adsorbent bed, and recovering the ultra pure product fromsaid third adsorbent bed; (v) terminating the flow of the displacedliquid regenerant to said first adsorbent bed and isolating said firstadsorbent bed, draining said displaced liquid regenerant from said firstadsorbent bed, passing a superheated regenerant vapor stream to saidfirst adsorbent bed at a temperature effective to desorb oxygenates fromthe solid adsorbent and recovering said oxygenates from said firstadsorbent bed in a spent regenerant vapor stream, and cooling said firstadsorbent bed by passing said liquid regenerant to the feed end of saidfirst adsorbent bed and recovering said liquid regenerant; (vi)terminating the flow of the liquid regenerant to said first adsorbentbed and periodically incrementing the process cycle of steps (iii)-(v)for said second and third adsorbent beds; and, (g) passing said ultrapure product from said oxygenate recovery zone into said firstseparation zone.
 11. The process of claim 10 wherein said etherificationfeedstream includes C₄ isoolefins, said monohydroxy alcohol of step (b)is methanol and said etherification zone produces MTBE.
 12. The processof claim 10 wherein said etherification feedstream includes C₄isoolefins, said monohydroxy alcohol of step (b) is ethanol and saidetherification zone product is ETBE.
 13. The process of claim 10 whereinsaid etherification feedstream is a dehydrogenation zone effluent streamthat includes C₁ -C₃ hydrocarbons and traces of hydrogen.
 14. Theprocess of claim 10 wherein said etherification contains a sulfonatedsolid resin catalyst and operates at a temperature in the range of from30°-100° C. (85°-210° F.) and a pressure of from 10-40 bars.
 15. Theprocess of claim 10 wherein said regenerant is comprised of at least aportion of said ultra pure product.
 16. The process of claim 10 step (f)wherein said solid adsorbent is activated alumina or a zeoliticmolecular sieve.
 17. The process of claim 10 step (f) wherein theadsorbent for the adsorbent beds is zeolite 13X.
 18. The process ofclaim 10 step (f) wherein the adsorbent beds operate at an adsorptioncondition of between 30° and 60° C.
 19. The process of claim 10 step (f)wherein the temperature of the superheated regenerant is between 240°and 315° C.
 20. The process of claim 10 step (f) wherein the ultra pureproduct contains between 1 and 0.1 ppm wt. oxygenates.
 21. The processof claim 10 step (f)(v) wherein the first adsorbent bed is drained bypassing a portion of the superheated regenerant vapor stream to theeffluent end of said first adsorbent bed to force displaced liquidregenerant from said first adsorbent bed.
 22. The process of claim 10step (f)(v) further comprising condensing the spent regenerant vaporstream to provide a hydrocarbon phase comprising regenerant andoxygenates and an aqueous phase comprising oxygenates recovering andsaid hydrocarbon phase and said aqueous phase.